There is a steady increase in the demand for automatic camera surveillance. For example, it is desirable to detect motion of objects in images captured by a camera even at long distances and under difficult circumstances. For that purpose, there is a large number of motion detection engines, being automatic systems for motion detection, commercially available on the market.
A motion detection engine may e.g. run on a network device, such as a server, and one or more cameras may stream a captured video stream of images to the network device via a network for subsequent motion detection. Due to bit rate limitations when streaming the video stream of images to the network device, the captured video stream of images is typically converted, such as being compressed or converted to a lower bit depth, prior to being sent to the network device. In other words, the number of bits representing the images in the video stream is reduced prior to transmission to the motion detection engine. By way of example, each pixel in an image in the video stream may be represented by 16 bits prior to conversion and 8 bits after conversion.
Due to the limited number of bits used to represent the images in the video stream on which the motion detection engine operates, the motion detection engine will have a limited capability of detecting small objects. For example, the small objects may disappear during the bit conversion process or, due to a low contrast in or a low resolution of images in the video stream on which the motion detection engine operates, a small object may be mistaken for noise, and may hence be removed by the motion detection engine.
UK patent application GB 2 442 512 A discloses a motion detector which operates on images received from a camera, i.e. images which typically have already been subject to bit conversion. The disclosed motion detector calculates differences between a current and previous video frames so as to detect edges of moving objects. In order to accentuate moving objects in comparison to noise, the detected edges are enhanced so that edges of true moving features score more highly than random pixel changes.
GB 2 442 512 A thus proposes to make changes in the motion detection algorithm in order to enhance true moving objects in comparison to random noise. With this approach it is hence ruled out that a standard, commercially available, motion detection engine may be used. Moreover, this approach suffers from the fact that already prior to being subject to motion detection, small objects may have been removed or disappeared from the images due to the bit conversion which typically takes place in the camera.
It would thus be desirable to be able to use a standard, commercially available, motion detection engine, and still improve the result of the motion detection with respect to detection of small objects covering a few pixels in the captured images.